Grizzly Bear, Alaska
As the northern hemisphere experiences the winter solstice, let’s take a look at how various wildlife species adapt to this season. It’s a fascinating picture, and each animal has a different story.
Some animals hibernate, some go into a more wakeful sleep called torpor, some barely lose a wink, and others migrate. For many creatures, the body changes.
Classic hibernators, like bears, eat large amounts of food in autumn to store fat for survival. They sleep all or part of the winter, and exist primarily on their fat stores. There is a slow-down of heart and respiration rate, and a lowering of the body temperature.
But few animal species have such a defined program–it varies by region, temperature, elevation, and other factors. And truth be told, even bears differ widely in their hibernating tactics.
Most big mammals have enough bulk that they do not hibernate. Bison, for example, simply grow a heavier coat to withstand freezing temperatures.
Shedding bison in back, Yellowstone NP
Bison in Lamar Valley on a snowy day, Yellowstone
Smaller mammals, however, are more inclined to hibernate because little bodies have a high surface-area-to-volume ratio; i.e. it takes more energy for a small animal to stay warm. Many small mammals burrow into the ground to wait out the foodless winter.
Marmot, Mt. Rainier, Washington
Marmots (aka groundhogs) build their fat storage and spend half their lives in hibernation. Prairie dogs, on the other hand, periodically come out of the burrow to munch on grass and then go back to sleep.
Prairie Dog at burrow, Colorado
Every species has a different physiological system for adapting to the food loss of winter.
Reptiles are cold-blooded and depend on the sunshine for metabolic activity.
Skink, California
In winter most reptiles in cold regions find a deep crack or rock cave and sleep through the months of sunless chill. They’re so inactive they don’t eat…don’t need to eat.
If you pick up a lizard who is essentially dormant, they only open their eyes in terror; but they do not move because they can’t.
Northern Alligator Lizard, California
Many species group together for warmth. They huddle while they sleep. That’s how we can sometimes come across a hole filled with snakes, or large colonies of bats.
Eastern Long-eared Bats, Australia
Some snakes and amphibians hibernate underneath water in locations where water doesn’t freeze. Certain snake species use their skin as a lung to extract oxygen from the water.
Even though toads and frogs stay quiet and resting most of the winter where I live, on a fluky mild winter day I will hear a toad call out from its burrow.
Western Toad in burrow, California
Insects transform into larvae, nymphs, eggs, or pupae forms to weather the winter. Others, like the monarch butterfly, migrate to warmer places.
Anise Swallowtail Chrysalis or Pupa
There is endless variation not only in species, but in location too. Here in northern California where the winter is mild, hovering close to freezing for only a month or two, I often discover winter wildlife anomalies.
I’ve read that praying mantis adults, for example, hide their eggs from predators for the winter and then die off. In spring the new insect emerges from the egg and starts the life cycle.
Not where I live. This photo of a loggerhead shrike in the California winter rain about to eat an adult praying mantis proves otherwise.
Loggerhead Shrike preying on a praying mantis, California in January
If winter temperatures do not fluctuate drastically, or are relatively mild, many insects find shelter and food in leaf litter, tree holes, under logs, or in soil or plant galls.
And don’t get me started on what the birds do. Some stay put if they live in a temperate zone, others migrate, and still others tough it out in cold regions. There is only one bird known to hibernate, the common poorwill.
Some birds and small mammals in arctic regions turn white in the frigid months to camouflage with snow. Their bodies adapt in numerous ways. Below are the summer and winter versions of the willow ptarmigan (bird) and snowshoe hare.
Willow ptarmigan, Alaska in August
Willow ptarmigan in winter plumage. Photo by John and Ivy Gibbons.
Snowshoe Hare in August, Alaska
Snowshoe Hare in winter. Photo by D. Gordon E. Robertson.
Whatever the season, nature not only has its curious, changing ways, but also unpredictability…just enough to keep the mystery and beauty alive.
Happy Solstice, Happy Holidays, dear reader.
Written by Jet Eliot.
All photos by Athena Alexander unless otherwise noted.
Mammalian tourists in winter
